PHOENIX — Never has “run differential” meant so much in the World Baseball Classic.

On Friday night it was key in what could have been Team USA’s elimination. And on Saturday afternoon at Chase Field, it was that tiebreak rule that led to one of the most ferocious baseball brawls ever and the first in the three editions of the WBC.

Once the benches of Mexico and Canada cleared, this wasn’t about defending teammates or an organization. This was about national pride, and the intensity of the brawl signified exactly that.

The Pool D game between the Canadians and Mexicans had hints of bad blood with hard slides and a home-plate collision, but both sides agreed that was hard-but-clean ball. But when Canada catcher Chris Robinson, producer of two of those previous hard slides and receiver of the home-plate collision, dropped down a bunt with a six-run lead in the top of the ninth inning, well, that wasn’t seen as good baseball by several of the Mexicans, who eventually lost, 10-3.

Mexico third baseman Luis Cruz picked up the bunt in disgust, looked at pitcher Arnold Leon, gestured to his ribcage, pointed to the oncoming hitter and could be seen in replays mouthing the Spanish word “pega” among other things. That roughly translates to “hit” or “beat” in English.

Leon heeded the command. He went after the next hitter, Rene Tosoni, with two fastballs that missed the left-handed hitter. After the second try, plate umpire Brian Gorman warned both benches. Leon didn’t heed that message and drilled Tosoni in the back with the next pitch.

Hell broke loose after that.

Mexico catcher Sebastian Valle gave a light shove to Tosoni as Tosoni walked toward Leon. Players came flying off both benches and from all positions on the field. Cruz raced into the middle of a mob and shot the first punch, and countless more followed from several different fists hailing from both countries.

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“I thought I saw Satan in his eyes,” said Canada first base coach Larry Walker, who had a hold of Aceves for a time.

Mexican center fielder Eduardo Arredondo was also caught letting his hands go freely and ended up where slighter-built men end up in a dog pile—at the bottom of several bigger Canadians, some chucking punches at his head.

Four Mexican players were ejected, three Canadians. Now, Major League Baseball and the players’ union, which make up the WBC committee, will huddle to figure out if suspensions need to be handed out.

Eventually a sense of order was restored, but that’s all it was. Just a sense.

As Team Canada meandered back to its first base dugout, starting pitcher Chris Leroux gestured to Mexican fans, either telling them to shut up or keep talking. Then he grabbed his jersey and popped the “CANADA” stitched across his chest.

Then someone from the stands threw a water bottle into the Canada bunch, hitting pitching coach Denis Boucher in the forehead. That prompted a couple of Canada players to try to climb atop the dugout and go after the perpetrator. They were stopped, and Maricopa County Sheriffs had to get involved after that.

Play resumed, and after a foul ball was hit down the right-field line, a fan threw the ball back onto the field and just missed hitting Walker with it. Canada manager Ernie Whitt told the umpires that if another thing was thrown onto the field, he was pulling his team off of it. As that was happening, Walker turned toward where the ball came from and he too popped his jersey at the fans.

“You can’t hurt us Canadians,” Whitt said.

Funny line, but the fight was hideous. There were acts of physical violence, stupidity and overall offenses worthy of banishment from this tournament in the future.

And almost all of it came from a “misunderstanding,” as Mexican manager Rick Renteria put it afterward.

“It was simply a misunderstanding,” Renteria said. “In a normal setting, a normal professional setting, a 9-3 (the score) bunt in that particular situation would be kind of out of the ordinary. But based on the rules that have been established in this tournament, the run differentials and things of that nature, it was talked about before that those things may occur.

“I think in the heat of the moment, you lose sight of it and maybe that’s how it occurred. It was just a misunderstanding.”

That is a troubling statement. First, there were two pitches that Leon threw at Tosoni before the third actually hit him. In that time, Renteria realized what was happening and could have prevented the “misunderstanding” by going out to talk to his infield, telling them that Canada isn’t trying to irk anyone, that it is just trying to look out for its own advancement in the format this tournament is played under.

But Renteria did nothing.

Second, other players on the Mexican team were aware of what and why Robinson dropped down the bunt with Cruz playing deep on him. If one player understood it after Renteria explained it before the team’s first game Thursday, then all of them should have realized. Cruz included. Leon included.

“Yeah, because we knew about (the rules) and the runs,” said Mexican pitcher Oliver Perez, who was ejected for his role in the melee. “When something like that happens, you feel mad, but in the same moment you have to understand that this is the style of baseball in this tournament.”

Canada certainly understood it, because about 24 hours earlier it was dominated by Italy by 10 runs, invoking the mercy rule. So its players understood the importance of run differential.

Understanding the rule, however, doesn’t necessarily mean one agrees with its place in the WBC.

“In this tournament, you play baseball like it’s 0-0,” Whitt said. “That’s the unfortunate thing. What happened tonight is because of the rulings that they have. Regular baseball, during the season, you would never see that happening, but because of the run differential that they have, you play it like a 0-0 game the whole time.

“They need to take a look at that.”

Renteria, Perez, Robinson and Justin Morneau all agreed. Team USA manager Joe Torre, who as Major League Baseball’s executive VP for baseball ops has a hand in things like MLB discipline and rules changes, wouldn’t comment if a new tiebreak rule is needed.

Perez made an accurate assessment of why the situation became volatile despite Canada not doing anything wrong under these rules. He noted that at the time, everything was going right for Canada, and Mexico couldn’t catch a break from the umps or make any for itself.

“It’s a lot of emotion,” said Perez, who was in the bullpen warming up when Tosoni was hit. “When things are going that way, things like that can happen.”

When the door is open to not only run up the score, but also stealing bases or bunting with a huge lead, it is inviting the opposing team to take offense at some point, right or wrong. It might happen once every three tournaments, but the ingredients for a powder keg like this are not just present, they are welcomed because of run differential. And when you throw nationalism into the mix for these proud men, things can escalate quickly.

The WBC craves attention, but MLB commissioner Bud Selig definitely doesn’t want this kind. So before something like this happens in 2017 or beyond, the convoluted tiebreak rules ought to change.